This invention relates to a perspective viewing system for automatic or visual soldering inspection wherein inspection of solder joints or display of solder joint images is performed utilizing angular bird""s eye perspective view images of solder joints of electronic parts mounted on a printed circuit board (PCB). The angular bird""s eye perspective view is attained by coordinated operations of an active vision system and a stage. In accordance with data taught, the active vision system views the board by bird""s eye perspective angles while the stage holds it in a pose presenting angular aspect to the active vision system.
Visual inspection of electronic products has been done with naked eyes or using a stereoscopic microscope, but with advanced miniaturization of parts, human inspection has become increasingly more difficult and more unreliable. Hence, demands for the automation have emerged nowadays to raise reliability and to save human cost.
Many kinds of apparatuses for automatic soldering inspection of electronic parts have been developed and already used in assembly lines. However, they have still problems not only in their external properties, for example, the bigger sizes, the heavier weights, and the higher costs than what had been expected but also in their inferior recognition ability as compared with humans. Their imperfect recognition is in close relationship with difficulties in tuning the discriminative parameters. Thus, problems in conventional apparatuses still remain to be solved.
Conventional machines were based on a variety of three-dimensional image measurement techniques, but their optical principles were common in their viewing directions. They fixed their view directions in an angle either vertical or very acute to objects (less than approximately 10xc2x0). As the result, they could not obtain but a top view or an almost top view of a solder joint for recognition. Their vertical viewing direction was a common deficit causing inferior recognition and difficulty in fine tuning. Depicted schematically in FIG. 13 is a typical top view image of a solder joint 32 produced between a printed pattern 30 and an LSI electrode tip 31.
The reason why they commonly and exclusively adopted a vertical view was that they had to use a magnifier lens to distinguish minimal differences in solder shapes. As an essential feature of a magnifier lens, the focal length is so short and focusing depth is so shallow that inspection apparatuses to date were subjected to a vertical view and forced to give up an oblique, perspective view. (A perspective view is attained with a lens of long focal length.)
It is generally accepted that we cannot obtain satisfactory information on three-dimensional shape only from. the top view. We experience this in our daily lifexe2x80x94we cannot know shape of a house from an aerial photo showing only the roof. A study of information theory has analyzed this relationship (see Reference 1: Kato, T., Sato, Y., and Shimizu, A., xe2x80x9cSelecting view direction based on range mapsxe2x80x9d (in Japanese), Technical report of Inst.Electron.Inf.Com.Eng., IE90-1, 1xcx9c8, 1990).
As the paper (Reference 1) analyzed it, information quantity obtainable from an image of a three-dimensional object depends largely upon the viewing direction. This is also true for human inspection of solder joints. A drop of solder fixes an electrode to a pad of a printed circuit pattern mainly at the bottom. Shape of solder fillets wetting the front and sides of an electrode reflects the soldering quality.
An inspector holds a board by hand, tilts it, and turns it under an illuminating light in order to discriminate solder shapes. This performance signifies nothing but an effort to obtain maximal amount of information from appearance. He/she looks obliquely down at part""s electrodes on a tilted and/or turned PCB, thus achieving an angular bird""s eye perspective view of solder joints.
Prior art of an active vision inspection apparatus with mirror motion was disclosed in Japan Patent Application No. Thkuganhei 8-20728 filed by the inventor. Following the prior art, the present invention intends to introduce an inspection system for parts-mounted and soldered PCBs wherein angular bird""s eye perspective view images are utilized for automatic or visual recognition.
An object of the present invention is to provide a perspective viewing inspection system capable of utilizing angular bird""s eye perspective view images of solder joints (as depicted in an angular bird""s eye view diagram of FIG. 13) for automatic discrimination, replacing top viewing of conventional techniques.
Another object of the present invention is to provide a perspective viewing inspection system capable of acquiring angular bird""s eye perspective view images of solder joints to display them on a monitor screen for visual image inspection.
In accordance with a feature of the present invention, a perspective viewing inspection system comprises a stage for holding a PCB mounted with electronic parts, teaching means for teaching position data and pose data of the PCB during inspection and also part electrodes"" addresses on the PCB, means for making inspection sequence programs, means for imaging, and means for evaluation, wherein said means for imaging includes an active vision system for acquiring bird""s eye perspective view images of the PCB and wherein said stage is equipped with a PCB pose controller for orienting the PCB at such an angle that said active vision system may obtain its angular perspective views, enabling angular bird""s eye perspective view imaging of solder joints for automatic evaluation of soldering quality.
In accordance with another feature of the present invention, a perspective viewing inspection system comprises a stage for holding a PCB mounted with electronic parts, teaching means for teaching position data and pose data of the PCB during inspection and also part electrodes"" addresses on the PCB, means for making inspection sequence programs, means for imaging, and means for display, means for superimposing markers on displayed inspection point images, and means for inputting results of visual image inspection, wherein said means for imaging includes an active vision system for acquiring bird""s eye perspective view images of the PCB and said stage is equipped with a PCB pose controller for orienting the PCB at such an angle that said active vision system may obtain angular perspective views of the PCB, enabling display of angular bird""s eye perspective view images of solder joints for visual image inspection.